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Alert Notice 321: Multicolor CCD campaign for AS 325 to support Spitzer observations

July 13, 2005

Summary
We request nightly BVRI CCD observations of the symbiotic eclipsing binary star AS 325 until December 1, 2005. The goal of the campaign is to determine the nature of this enigmatic system by looking for changes in color during the current eclipse and also to support upcoming observations with the Spitzer Space Telescope planned for September.

AS 325 is at R.A. = 18:50:03.6 Dec. = -26:24:18 (2000).

Background
AS 325, also known as NSV 24607 and with AAVSO designation 1843-26, is an eclipsing binary star with a 513d period. It has unique emission lines that have defied easy classification and made it an object of interest for amateur and professional astronomers alike.

The next Algol-type eclipse of AS 325 has already begun and is expected to be centered on July 18, 2005. In addition, the system's mean brightness is also slowly increasing and short term flickering on the order of days is seen. So there are lots of things to observe in this system.

S. Otero (OSE) studied the star in detail using ASAS-3 survey data and published his results, along with historical detail, in IBVS #5608. The paper can be found at the following URL:

Dr. Steve Howell has taken spectra recently with the WIYN observatory and found the H emission is 50% weaker while the Fe II lines remain constant. In addition, previously detected strong Ca II H&K absorption lines are absent. Howell has approved time on the Spitzer Space Telescope to observe the object in September or October. He is also continuing his ground based spectra observations next week and into the fall as well.

Observations
CCD observations in BVRI are valuable because the system seems to be changing color during the eclipses. In addition, the changing strength of the emission lines will affect measurements in different filters in different ways. So good quality BVRI datasets can tell us much about this system.

We ask for one observation per night in each of the BVRI filters. If you do not have all the filters then use the ones you do have. Aim for 0.01 accuracy. Since time series is not needed and the system is fairly bright it should be relatively easy to get a good SNR.

This field is in Sagittarius so is appropriately crowded. We did our best to choose comparison stars without companions but it was not always possible. Choosing your aperture settings will be important. Do not let the boundary of an aperture annulus fall on any star. Either leave the companion out or include it entirely in the annulus. Take careful note of the aperture sizes you use in your photometry and ** use the same aperture setting each time you observe **! This is important for consistency.

According to ASAS-3, AS 325 is currently around magnitude V=12.0. Its most recent eclipses dipped to around magnitude V=11.4 but this eclipse is obviously already fainter than that. We are not sure how faint AS 325 will go. It's up to you to observe and find out for us!

An AAVSO chart with V-band comparison stars is available at the following URL:

Arne Henden is expected to calibrate the field in BVRI in the next few weeks. We will update the chart when that data is available. Go ahead and observe now in BVRI and just hold on to the BRI data until we have updated the chart with full color comparison stars. Then process and send the BRI observations in.

A paper will be written about these observations and, as per regular AAVSO policy, all who significantly contribute to the campaign will be included as co-authors.